Business Combinations - Results of Operations (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual			$ 21,452
Business Combination Pro Forma Information Income Loss Before Income Taxes Of Acquiree Since Acquisition Date Actual			2,375
Total revenues	$ 462,684	$ 445,672	1,350,014	$ 1,295,027
Income before income taxes	117,144	115,749	332,101	315,824
Net income	$ 71,650	$ 69,171	$ 201,996	$ 190,387
Net income per share:
Basic (in dollars per share)	$ 0.51	$ 0.49	$ 1.45	$ 1.35
Diluted (in dollars per share)	$ 0.51	$ 0.48	$ 1.43	$ 1.32
Weighted Average Basic Shares Outstanding, Pro Forma	136,461	137,684	136,002	138,181
Weighted average number of shares outstanding:
Pro Forma Weighted Average Shares Outstanding, Diluted	138,182	140,041	137,584	140,446